In order to analyze working principle and stability error of double longitudinal-mode He-Ne laser with stabilization frequency,a requirement is put forward,which is that an intracavity laser with cavity of 100～300 mm length can produce double longitudinal-mode light.According to laser working process,stabilization frequency includes mode hopping,transition stage and stabilized mode.With laser principle and thermodynamic theory,mechanism of stabilization frequency of the laser is interpreted on the basis of output voltages of the two photodiodes.Beat frequency test shows that frequency stability of He-Ne laser is 5×10^-10.Based on error analysis,the frequency stability of He-Ne laser is only influenced by change of resonant cavity length.Furthermore,increasing length of the resonant cavity can lead to higher frequency stability.The laser with double longitudinal-mode stabilized frequency has a shorter locked time.